Eye Dictionary: L
L
lacrimal gland. The lacrimal gland is a tear-producing gland that is located in the upper eyelid, underneath the orbital bony ridge (i.e., under the bone that makes the upper eye socket). Most people think that the lacrimal gland is the main source of tears. Actually, that's not quite true. Most of the tears that cover our eyes are made by small accessory glands that cover the entire conjunctiva (the skin over the white of the eye) and under the eyelids. These little glands continuously excrete tears and create our "basal tear rate." The lacrimal gland is mostly responsible for reflexive tearing ... the tears that come out when crying or when the eyes are irritated. Many people with chronically dry eye complain that their eyes seem to water all the time. For these people, their basal tear rate is low so their eyes dry out and "sting" a little bit. This stinging causes the lacrimal gland to reflexively dump out all its tears at once, leading to episodes of excessive watering followed by periods of relative dryness. By breaking this dry-wet cycle with regular use of artificial tears, the lacrimal gland can calm down and decrease these unnecessary tearing episodes.
laser. Laser stands for "Light Amplification by Stimulated Emission of Radiation" (in case you were interested). Lasers work by amplifying light (or non-visible radiation) of a single wavelength. This can create a highly controllable beam of energy which can be used to burn, cut, or ablate tissues in the body. There are many uses for lasers in ophthalmology. The most obvious one is LASIK surgery, where a laser can be used to sculpt the surface of the cornea and fix a person's glasses prescription. Lasers are also used for treating after-cataracts, an opacity that can form after cataract surgery. The retina can be treated with a laser, and microaneurysms and edema from diabetic retinopathy can also be treated with a laser to stop the leakage (see FLT laser for more details). Retinal detachments can be "tacked down" with laser spots to keep the retina from peeling off further.
LASIK. This is a procedure where the cornea is sculpted with a laser in order to fix refractive error and decrease reliance on glasses. The cornea is the clear window that makes up the front of your eye. Surprisingly, the corneal surface does the majority of the light-focusing of the eye (not the lens inside the eye like you might expect). People with flat corneas have "weaker" powered eyes (hyperopia or farsightedness) while people with steep corneas have "over-powered" eyes (myopia or nearsightedness). With LASIK, a special excimer laser is used to obliterate tissue and sculpt the cornea into the correct steepness. To minimize pain and inflammation, the laser is not applied directly to the surface of the eye. Instead, a partial thickness cut is made in the cornea to create a "flap." This flap is opened like a trapdoor to expose deeper layers of the corneal stroma underneath. The laser is then applied to this area to remove corneal tissue. When done, the corneal flap is flipped back over and "squeegeed" back into place to heal. While this may seem unnecessarily complicated, this flap method decreases inflammation and speeds healing time because the surface corneal epithelium is relatively intact. Because the treatment area is deep in the corneal tissue, it is more protected from problems (like scarring) while healing. There have been some more recent advances in the LASIK procedure ... one is Intralase where a femtosecond laser is used to create the flap (instead of the original microkeratome blade of the past). Not everyone is a good candidate for LASIK, such as those with keratoconus or naturally thin corneas (as measured by pachymetry). PRK is a similar to LASIK, but the laser is applied directly to the surface of the eye and thus has more postoperative discomfort and more potential for corneal haze (scaring).
Lastacaft. A prescription strength allergy drop good for treating swelling and itchy eyes. It is supposed to last about 16 hours, so is usually dosed once a day. Alternative prescription allergy drops include Bepreve and Pataday.
latanoprost. This is a prostaglandin eye drop used for treating glaucoma. The trade name is Xalatan. For many doctors, latanoprost is the first-line drop used in glaucoma because of its powerful effect and easy once-a-day dosing.
Latisse. This is a topical medicine used to make the eyelashes grow longer. This drug is the same medicine used in the glaucoma drop Lumigan (bimatoprost). Eyelash growth is a known side effect of prostaglandin glaucoma drops and Allergan is capitalizing on this with their topical product. Latisse is typically applied to the upper eyelid at night. While effective, especially compared to the "holistic" eyelash treatments on the market, there are some real side effects with this medicine you need to be aware of. First, the medicine can increase the pigmentation of the skin around the eyes, especially with long-term use. Another is that prostaglandins can cause a certain amount of redness and irritation to the eye itself - this is why it is applied at night so that you can sleep through any irritation. Also, this medicine can darken the eye color (the iris color) especially in people with hazel-colored eyes. Admittedly, we don't see these complications often in our practice, despite a large number of our patients on glaucoma drops. For our glaucoma patients the potential side effects are easy to justify - as glaucoma can cause blindness if not well-treated.
lattice degeneration. This is a thinning of the peripheral retinacommonly found during a dilated eye exam. People with thinning retinasare at slightly higher risk for developing a retinal detachment in theirlifetime. This localized area of atrophy is predisposed to forming holes ortears (especially after a vitreous detachment) that can extend into the rest of the eye. Lattice degeneration is very common with about 5% of the population demonstrating this finding, especially in people with large amounts of nearsightedness.
lazy eye. This is an eye that doesn't see well but is otherwise healthy. This occurs from disuse at a young age when the visual nervous system is still forming. See amblyopia for more information on this topic.
legal blindness. In North America, the definition of legal blindness is vision that is 20/200 or less in the best seeing eye, despite using the best correction possible (i.e., up-to-date glasses). A 20/200 vision measurement on the Snellen chart means that if a "legally blind person" stood 20 feet away from a vision chart, they could read only as good as a "normal person" standing 200 feet away. Another definition of legal blindness is used for people with severely constricted peripheral vision (typically 20 degrees or less). These people may have good central vision on an eye chart, but their peripheral vision is so constricted that its like they are looking through a "soda straw." This amount of vision is unsafe for driving (or duck hunting) so it is also called "legal blindness."
lens. The lens is the magnifying glass inside our eye that controls fine focusing. The lens is located immediately behind the iris (the colored part of the eye). Like the cornea, it is living tissue yet it is clear. When light enters the eye, it travels through the pupil, then through the lens, before striking the retina in the back of the eye. The lens is held in place by little springs called zonules. These are arranged in a 360-degree ring around the lens "equator" and suspend the lens like a trampoline. A muscle called the ciliary body pulls on the zonules which controls the lens shape. This shape-changing ability is called accommodation, which is how we focus to see things close up. In youth, the lens is naturally soft and can change shape like a piece of Jell-O or gummy candy. This gives children a very wide range of focus as their lens can flatten like a 'pancake' to give far distance vision, or the lens can become round like a 'marble' to focus on the tip of a nose. As we age, the clear lens tissue begins to stiffen, and has a harder time changing shape. This process is called presbyopia, and explains why we start needing reading glasses around age 40. The lens eventually becomes cloudy, forming a cataract. When we repair a cataract, we create a hole in the front layer of the lens and remove the inner layers of the lens. A new plastic implant lens is then placed inside the husk of the original cataract lens. This new implant is optically clear, but made of plastic that can't change shape, so most are therefore set for one focus (to give good distance vision).
lensometer. A machine used in an eye doctor's office that can measure the prescription in an existing pair of glasses. Some are manual and others are automated machines. Knowing your current glasses prescription gives us a starting point when performing refraction (checking your vision on the eye chart). This measurement also allows us to advise you whether it's worth it to update your spectacles ... after all, if your new prescription is the same as your existing glasses, you might not
want to bother purchasing another pair.
levobunolol. A glaucoma eye drop. This is a beta-blocker similar to the eye drop timolol. This drop is generic and inexpensive, but I don't use it often as timolol is readily available.
lidocaine. This is an anesthetic liquid that is commonly injected into the skin prior to surgical procedures. I use it most commonly with chalazion excisions or when removing a papilloma from the eyelid. We inject lidocaine inside the eye during cataract surgery to numb the iris. On occasion, I will inject the medication behind the eye when performing a retrobulbar block - these blocks are only performed prior to difficult cataract surgeries, however.
lid scrubs. This is a technique for cleaning the eyelids in order to improve comfort, especially in cases of blepharitis. Debris can form on the eyelashes. This debris is typically made of dead skin cells and dried-up tear secretions. It is harmless, but bacteria living on our skin like to eat this debris because it is like "free lunch" to them. These bacteria create their own waste products that irritate the skin of the eyelids, making them puffy, red, and giving the eyes a sandy sensation. This is called
blepharitis and is very common. If we improve our lid "hygiene" and remove some of this debris, the eyes will feel better and less irritated. There are many ways to accomplish this. You can take a soft washcloth, dip it in warm water and add a little baby shampoo, and use this to gently scrub the lash line (with the eyes closed of course). You can also make a mixture of diluted baby shampoo and do the same regimen with cotton balls. Finally, there are pre-made pads such as the OCuSOFT pads, that are already prepared and ready for use. I usually recommend doing this lid scrub only once a day (though some people prefer more often). If you wash your lashes too often you may reach a point where your scrubbing regimen is irritating the lids more than it is actually helping.
Lotemax. This is the trade name for the steroid loteprednol. This steroid eye drop is commonly used after cataract surgery and in cases of ocular inflammation. While not quite as strong as prednisolone, Lotemax is touted as a safer medicine as it has less steroid side effects like
increased eye pressure.
loteprednol. A popular steroid eye drop that is usually packaged under the trade name Lotemax. This drop is commonly used in cases of ocular inflammation and for use after eye surgery to cool the eye down. This drug is also available in lower concentrations in the drop Alrex.
low-tension glaucoma. This is glaucoma that occurs despite the eye pressure being "normal." Glaucoma is normally defined as high intraocular pressure that causes damage to the optic nerve over many years. The underlying mechanism behind glaucoma is poorly understood but high pressure seems to be the main instigator. Some people seem to be exquisitely sensitive to mild pressure and develop nerve damage despite their eye pressure being in the "normal" range (10 to 21). These people require treatment to keep pressures very low. This is done with eye drops, lasers, and rarely glaucoma surgery.
LPI. This is the abbreviation for Laser Peripheral Iridotomy, a laser procedure performed on people who are at risk for having an acute glaucoma attack. To understand the purpose behind this procedure, it can be useful to think of the eye like a kitchen sink full of water. There is a "faucet" running at all times inside the eye that produces aqueous fluid. This fluid keeps the eye inflated like a water balloon and working properly. There is also a "drain" in the eye called the trabecular meshwork where the aqueous fluid drains away. It is the balance of this fluid input and output that determines the eye's pressure. The eye's drain is located in a 360-degree ring at the intersection of the iris (colored part of the eye) with the sclera (the white part of the eye). This intersection is commonly called the "angle" because it is a rather tight intersection with little excess room. Some people's ocular anatomy is such that their drainage angle is extremely tight and narrow. Under most situations, aqueous fluid can still drain out this tight junction ... but if conditions are just right, the drainage angle may shut closed entirely. With the drainage pathway blocked, the eye pressure will shoot up and cause intense pain with vision loss from acute glaucoma. This is always a bad situation
most people come into the office bent over and throwing up from the pain. Even with prompt treatment there is usually some permanent vision loss. For people who appear to have narrow angles, a prophylactic LPI is sometimes recommended. With this procedure a laser is used to create a small hole through the iris. This helps equalize the pressures inside the eye and dramatically decreases the chance of having an acute glaucoma episode. The laser procedure is quick, and for the most part harmless, though there are a couple of risks to be aware of. The main one is visual side effects afterwards. By creating a hole in the iris, this creates a secondary pupil that light can pass through to reach the retina. Some people complain of a ghost image or line around lights at night. This is rare, and we strive to keep the LPI hole very small and up under the eyelid to minimize this possibility. This must be considered and weighed against the possibility of a potentially blinding glaucoma attack.
Lucentis. This is an injectable anti-VEGF medicine used primarily to treat wet macular degeneration. It works by decreasing fluid release from leaking blood vessels under the retina. Lucentis is touted as being a more selective medicine than its competitor Avastin (and Lucentis costs a premium for this reason).
Lumigan. A prostaglandin eye drop used for treating glaucoma. The active ingredient is bimatoprost. Like all the prostaglandins, this medicine is dosed only once a day and usually taken in the evening. Similar medications include Xalatan (latanoprost) and Travatan (travoprost).
lutein. This is a yellow pigment created by plants that is absorbed and used by animals. Lutein is found in animal fats and is what gives egg yolks that yellow color. It is found in the retina along with another similar pigment called zeaxanthin. Lutein and zeaxanthin supplementation has been studied and found to be beneficial with macular degeneration (see the AREDS 2 Study for more information on this topic).
laser. Laser stands for "Light Amplification by Stimulated Emission of Radiation" (in case you were interested). Lasers work by amplifying light (or non-visible radiation) of a single wavelength. This can create a highly controllable beam of energy which can be used to burn, cut, or ablate tissues in the body. There are many uses for lasers in ophthalmology. The most obvious one is LASIK surgery, where a laser can be used to sculpt the surface of the cornea and fix a person's glasses prescription. Lasers are also used for treating after-cataracts, an opacity that can form after cataract surgery. The retina can be treated with a laser, and microaneurysms and edema from diabetic retinopathy can also be treated with a laser to stop the leakage (see FLT laser for more details). Retinal detachments can be "tacked down" with laser spots to keep the retina from peeling off further.
LASIK. This is a procedure where the cornea is sculpted with a laser in order to fix refractive error and decrease reliance on glasses. The cornea is the clear window that makes up the front of your eye. Surprisingly, the corneal surface does the majority of the light-focusing of the eye (not the lens inside the eye like you might expect). People with flat corneas have "weaker" powered eyes (hyperopia or farsightedness) while people with steep corneas have "over-powered" eyes (myopia or nearsightedness). With LASIK, a special excimer laser is used to obliterate tissue and sculpt the cornea into the correct steepness. To minimize pain and inflammation, the laser is not applied directly to the surface of the eye. Instead, a partial thickness cut is made in the cornea to create a "flap." This flap is opened like a trapdoor to expose deeper layers of the corneal stroma underneath. The laser is then applied to this area to remove corneal tissue. When done, the corneal flap is flipped back over and "squeegeed" back into place to heal. While this may seem unnecessarily complicated, this flap method decreases inflammation and speeds healing time because the surface corneal epithelium is relatively intact. Because the treatment area is deep in the corneal tissue, it is more protected from problems (like scarring) while healing. There have been some more recent advances in the LASIK procedure ... one is Intralase where a femtosecond laser is used to create the flap (instead of the original microkeratome blade of the past). Not everyone is a good candidate for LASIK, such as those with keratoconus or naturally thin corneas (as measured by pachymetry). PRK is a similar to LASIK, but the laser is applied directly to the surface of the eye and thus has more postoperative discomfort and more potential for corneal haze (scaring).
Lastacaft. A prescription strength allergy drop good for treating swelling and itchy eyes. It is supposed to last about 16 hours, so is usually dosed once a day. Alternative prescription allergy drops include Bepreve and Pataday.
latanoprost. This is a prostaglandin eye drop used for treating glaucoma. The trade name is Xalatan. For many doctors, latanoprost is the first-line drop used in glaucoma because of its powerful effect and easy once-a-day dosing.
Latisse. This is a topical medicine used to make the eyelashes grow longer. This drug is the same medicine used in the glaucoma drop Lumigan (bimatoprost). Eyelash growth is a known side effect of prostaglandin glaucoma drops and Allergan is capitalizing on this with their topical product. Latisse is typically applied to the upper eyelid at night. While effective, especially compared to the "holistic" eyelash treatments on the market, there are some real side effects with this medicine you need to be aware of. First, the medicine can increase the pigmentation of the skin around the eyes, especially with long-term use. Another is that prostaglandins can cause a certain amount of redness and irritation to the eye itself - this is why it is applied at night so that you can sleep through any irritation. Also, this medicine can darken the eye color (the iris color) especially in people with hazel-colored eyes. Admittedly, we don't see these complications often in our practice, despite a large number of our patients on glaucoma drops. For our glaucoma patients the potential side effects are easy to justify - as glaucoma can cause blindness if not well-treated.
lattice degeneration. This is a thinning of the peripheral retinacommonly found during a dilated eye exam. People with thinning retinasare at slightly higher risk for developing a retinal detachment in theirlifetime. This localized area of atrophy is predisposed to forming holes ortears (especially after a vitreous detachment) that can extend into the rest of the eye. Lattice degeneration is very common with about 5% of the population demonstrating this finding, especially in people with large amounts of nearsightedness.
lazy eye. This is an eye that doesn't see well but is otherwise healthy. This occurs from disuse at a young age when the visual nervous system is still forming. See amblyopia for more information on this topic.
legal blindness. In North America, the definition of legal blindness is vision that is 20/200 or less in the best seeing eye, despite using the best correction possible (i.e., up-to-date glasses). A 20/200 vision measurement on the Snellen chart means that if a "legally blind person" stood 20 feet away from a vision chart, they could read only as good as a "normal person" standing 200 feet away. Another definition of legal blindness is used for people with severely constricted peripheral vision (typically 20 degrees or less). These people may have good central vision on an eye chart, but their peripheral vision is so constricted that its like they are looking through a "soda straw." This amount of vision is unsafe for driving (or duck hunting) so it is also called "legal blindness."
lens. The lens is the magnifying glass inside our eye that controls fine focusing. The lens is located immediately behind the iris (the colored part of the eye). Like the cornea, it is living tissue yet it is clear. When light enters the eye, it travels through the pupil, then through the lens, before striking the retina in the back of the eye. The lens is held in place by little springs called zonules. These are arranged in a 360-degree ring around the lens "equator" and suspend the lens like a trampoline. A muscle called the ciliary body pulls on the zonules which controls the lens shape. This shape-changing ability is called accommodation, which is how we focus to see things close up. In youth, the lens is naturally soft and can change shape like a piece of Jell-O or gummy candy. This gives children a very wide range of focus as their lens can flatten like a 'pancake' to give far distance vision, or the lens can become round like a 'marble' to focus on the tip of a nose. As we age, the clear lens tissue begins to stiffen, and has a harder time changing shape. This process is called presbyopia, and explains why we start needing reading glasses around age 40. The lens eventually becomes cloudy, forming a cataract. When we repair a cataract, we create a hole in the front layer of the lens and remove the inner layers of the lens. A new plastic implant lens is then placed inside the husk of the original cataract lens. This new implant is optically clear, but made of plastic that can't change shape, so most are therefore set for one focus (to give good distance vision).
lensometer. A machine used in an eye doctor's office that can measure the prescription in an existing pair of glasses. Some are manual and others are automated machines. Knowing your current glasses prescription gives us a starting point when performing refraction (checking your vision on the eye chart). This measurement also allows us to advise you whether it's worth it to update your spectacles ... after all, if your new prescription is the same as your existing glasses, you might not
want to bother purchasing another pair.
levobunolol. A glaucoma eye drop. This is a beta-blocker similar to the eye drop timolol. This drop is generic and inexpensive, but I don't use it often as timolol is readily available.
lidocaine. This is an anesthetic liquid that is commonly injected into the skin prior to surgical procedures. I use it most commonly with chalazion excisions or when removing a papilloma from the eyelid. We inject lidocaine inside the eye during cataract surgery to numb the iris. On occasion, I will inject the medication behind the eye when performing a retrobulbar block - these blocks are only performed prior to difficult cataract surgeries, however.
lid scrubs. This is a technique for cleaning the eyelids in order to improve comfort, especially in cases of blepharitis. Debris can form on the eyelashes. This debris is typically made of dead skin cells and dried-up tear secretions. It is harmless, but bacteria living on our skin like to eat this debris because it is like "free lunch" to them. These bacteria create their own waste products that irritate the skin of the eyelids, making them puffy, red, and giving the eyes a sandy sensation. This is called
blepharitis and is very common. If we improve our lid "hygiene" and remove some of this debris, the eyes will feel better and less irritated. There are many ways to accomplish this. You can take a soft washcloth, dip it in warm water and add a little baby shampoo, and use this to gently scrub the lash line (with the eyes closed of course). You can also make a mixture of diluted baby shampoo and do the same regimen with cotton balls. Finally, there are pre-made pads such as the OCuSOFT pads, that are already prepared and ready for use. I usually recommend doing this lid scrub only once a day (though some people prefer more often). If you wash your lashes too often you may reach a point where your scrubbing regimen is irritating the lids more than it is actually helping.
Lotemax. This is the trade name for the steroid loteprednol. This steroid eye drop is commonly used after cataract surgery and in cases of ocular inflammation. While not quite as strong as prednisolone, Lotemax is touted as a safer medicine as it has less steroid side effects like
increased eye pressure.
loteprednol. A popular steroid eye drop that is usually packaged under the trade name Lotemax. This drop is commonly used in cases of ocular inflammation and for use after eye surgery to cool the eye down. This drug is also available in lower concentrations in the drop Alrex.
low-tension glaucoma. This is glaucoma that occurs despite the eye pressure being "normal." Glaucoma is normally defined as high intraocular pressure that causes damage to the optic nerve over many years. The underlying mechanism behind glaucoma is poorly understood but high pressure seems to be the main instigator. Some people seem to be exquisitely sensitive to mild pressure and develop nerve damage despite their eye pressure being in the "normal" range (10 to 21). These people require treatment to keep pressures very low. This is done with eye drops, lasers, and rarely glaucoma surgery.
LPI. This is the abbreviation for Laser Peripheral Iridotomy, a laser procedure performed on people who are at risk for having an acute glaucoma attack. To understand the purpose behind this procedure, it can be useful to think of the eye like a kitchen sink full of water. There is a "faucet" running at all times inside the eye that produces aqueous fluid. This fluid keeps the eye inflated like a water balloon and working properly. There is also a "drain" in the eye called the trabecular meshwork where the aqueous fluid drains away. It is the balance of this fluid input and output that determines the eye's pressure. The eye's drain is located in a 360-degree ring at the intersection of the iris (colored part of the eye) with the sclera (the white part of the eye). This intersection is commonly called the "angle" because it is a rather tight intersection with little excess room. Some people's ocular anatomy is such that their drainage angle is extremely tight and narrow. Under most situations, aqueous fluid can still drain out this tight junction ... but if conditions are just right, the drainage angle may shut closed entirely. With the drainage pathway blocked, the eye pressure will shoot up and cause intense pain with vision loss from acute glaucoma. This is always a bad situation
most people come into the office bent over and throwing up from the pain. Even with prompt treatment there is usually some permanent vision loss. For people who appear to have narrow angles, a prophylactic LPI is sometimes recommended. With this procedure a laser is used to create a small hole through the iris. This helps equalize the pressures inside the eye and dramatically decreases the chance of having an acute glaucoma episode. The laser procedure is quick, and for the most part harmless, though there are a couple of risks to be aware of. The main one is visual side effects afterwards. By creating a hole in the iris, this creates a secondary pupil that light can pass through to reach the retina. Some people complain of a ghost image or line around lights at night. This is rare, and we strive to keep the LPI hole very small and up under the eyelid to minimize this possibility. This must be considered and weighed against the possibility of a potentially blinding glaucoma attack.
Lucentis. This is an injectable anti-VEGF medicine used primarily to treat wet macular degeneration. It works by decreasing fluid release from leaking blood vessels under the retina. Lucentis is touted as being a more selective medicine than its competitor Avastin (and Lucentis costs a premium for this reason).
Lumigan. A prostaglandin eye drop used for treating glaucoma. The active ingredient is bimatoprost. Like all the prostaglandins, this medicine is dosed only once a day and usually taken in the evening. Similar medications include Xalatan (latanoprost) and Travatan (travoprost).
lutein. This is a yellow pigment created by plants that is absorbed and used by animals. Lutein is found in animal fats and is what gives egg yolks that yellow color. It is found in the retina along with another similar pigment called zeaxanthin. Lutein and zeaxanthin supplementation has been studied and found to be beneficial with macular degeneration (see the AREDS 2 Study for more information on this topic).